Musa (PROSEA Fruits)

Plant Resources of South-East Asia Introduction

List of species

Musa L. (edible cultivars)

Protologue: Sp. Pl.: 1043 (1753), Gen. Pl. ed. 5: 466 (1754).

Family: Musaceae

Chromosome number: x= 11 (diploid, triploid and tetraploid cultivars occur)

• Banana (En)
• Bananier (Fr)
• Indonesia, Malaysia: pisang
• Papua New Guinea: banana (Pidgin)
• Philippines: saging
• Burma: nget pyo thee
• Cambodia: cheek nam' vaa
• Laos: kwàyz
• Thailand: kluai
• Vietnam: chuôí.

The exact origin of the edible bananas is unknown. Simmonds and Shepherd proposed a theory which is generally accepted: the Indo-Malesian region is considered as the main centre of diversity, Malesia probably being the primary centre.

According to the theory, Musa acuminata Colla, a wild diploid banana with seeded fruit native to Malesia, is the major parent of most edible bananas, which arose in the first instance through the development of parthenocarpy and sterility. Human selection and vegetative propagation played an important role in the evolution of the edible bananas. Triploid forms presumably emerged through chromosome restitution; as they are more vigorous than the diploids, they have become very prominent.

From time to time further outcrossing of these edible diploid and triploid forms of M. acuminata must have occurred, not only backcrossing with the parent species, but also hybridization with Musa balbisiana Colla, another wild diploid species with seeded fruit which occurs from India to the Philippines and New Guinea, but is absent in central Malesia. Through processes similar to those described, hybridization gave rise to diploid, triploid and tetraploid hybrids; natural tetraploids are rare. These hybrids grow better in drier areas than M. acuminata types and are resistant to some diseases.

Whereas Simmonds and Shepherd are of the opinion that the above forms cover all the edible bananas, others contend that developments parallel to those in the wild M. acuminata occurred in M. balbisiana , bringing edible diploid and triploid forms of the latter into existence, which have been taken into cultivation. This view is followed here.

From South-East Asia the cultivation of banana has spread throughout the tropics and into the subtropics of Asia, America, Africa and Australia; in fact the banana is cultivated wherever it will grow and bear fruit.

The fruit is the main product. It is used either raw or cooked, or prepared in another way. It may be processed into starch, chips, puree, beer (Africa), vinegar, or it may be dehydrated. The male buds of some cultivars (e.g. "Saba") are used as a vegetable.

The leaves are used to polish floors, to line pots in which rice is cooked and as wrappers for various foods. Fibres for making cloth can be obtained from the pseudostem. Vegetative parts as well as reject fruit are used as fodder, the former particularly when forage and water are scarce (the pseudostem contains much water). The plant - or its leaves and fruits - also plays a part in cultural traditions; in Indonesia, for example, at weddings, when a house is erected and locally in religious ceremonies.

Medicinally, the young unfolded leaves are used against chest pains and as a cool dressing for an inflamed or blistered skin. The sap exuding from the base of the cut trunk is used for urethral injections against gonorrhoea, dysentery and diarrhoea; it is also used to stop the loss of hair and to stimulate its growth. The juice of the root is febrifuge and restorative. In powder form, it is used in cases of anemia and general weakness and malnutrition. The unripe fruit is a part of the diet for persons suffering from haemoptysis and diabetes. In the dried state, it is antiscorbutic. The fully ripe fruit is a laxative when taken early in the morning. The flour made from banana is used for dyspepsia with flatulence and acidity.

The world production of bananas in about 120 countries is estimated to be over 68 million t annually. The banana is the most important fruit species in South-East Asia, ranking first in the Philippines, Indonesia and Thailand, in both area and production. Statistics for 1987: the Philippines 3 755 000 t from 330 500 ha; Indonesia 2 192 000 t from 175 600 ha; Thailand 471 500 t from 183 500 ha; Malaysia 186 900 t from 27 700 ha. It is one of the most important export crops in the Philippines and Malaysia, bringing in an estimated US$ 120 million and US$ 2.87 million respectively in 1987.

Banana growing has been adapted to systems ranging from shifting cultivation to corporate plantations; the most common form of production in South-East Asia is home gardening.

Fruits of various cultivars differ in their nutritional composition. At fruit maturity 100 g edible portion contains approximately: water 70 g, protein 1.2 g, fat 0.3 g, carbohydrates 27 g, fibre 0.5 g. It is rich in potassium (400 mg/100 g) and has a special place in diets low in fats, cholesterol and salt. It is also a good source of vitamin C and vitamin B6 with trace amounts of vitamin A, thiamine, riboflavin and niacin. The energy value of ripe banana ranges from 275 to 465 kJ/100 g.

• Tree-like perennial herb, 2-9 m tall, with a short underground stem (corm) with buds, from which short rhizomes grow to produce a clump of aerial shoots (suckers) close to the parent plant.
• Roots adventitious, spreading 4-5 m laterally, descending to 75 cm, but mainly in the top 15 cm, forming a dense mat.
• Shoots cylindrical pseudostems of overlapping leaf-sheaths which are tightly rolled round each other to form a rigid bundle of 20-50 cm diameter.
• New leaves originating from the corm grow up continuously through the centre of the pseudostem with their laminas tightly rolled.
• The emerging leaf unfolds a large oblong blade, 150-400 cm × 70-100 cm, with a pronounced supporting midrib and well-marked, pinnately arranged, parallel veins.
• One terminal inflorescence rises from each corm, its axis (peduncle) extending through the centre of the pseudostem and bending down when exserted; it is a compound spike of flowers which are arranged in several groups, compact and conical when young; each group is enclosed in a large ovate, pointed reddish bract and consists of two closely appressed rows of flowers; the bracts become reflexed when the flowers develop and they are shed when the fruits start to develop; female flowers develop proximally, male flowers at the distal end of the inflorescence, in the middle sometimes neuter flowers are present; commonly 12-20 flowers are produced per node, and usually 5-15 nodes produce female flowers; the bracts open in sequence (about 1 per day) from base to top while the peduncle elongates; finally the mature infructescence is about 50-150 cm long, bearing hands of fruits, followed by a long bare axis formed if - as in most cultivars - the male flowers and subtending bracts abscise, terminating in a growing point ("male bud") which continues to produce bracts and male flowers.
• Female flowers (about 10 cm long) have an inferior ovary of 3 united carpels, roughly triangular in section, surmounted by a short perianth of 5 fused segments and 1 free segment, which together form a tube around the style and the sterile androecium; stigma 3-lobed; staminodes 5; male flowers about 6 cm long, stamens 5, rarely bearing pollen, pistillode small.
• Fruit berry-like, seedless, 6-35 cm × 2.5-5 cm, curved, green, yellow or reddish; each cluster of fruits at a node is a "hand" and individual fruits are "fingers".

Branching of the rhizome is sympodial: the apical meristem expends itself in flowering and fruiting; lateral shoots (on emergence called "peepers", later "suckers") emerge from buds on the corm, situated opposite the leaf axils, to repeat the process. These side shoots are short and turn upright as soon as they are clear from the mother corm, so that a compact clump of shoots is formed. Suckers emerge mainly from buds on the middle and upper parts of the corm. Thus, successive generations of suckers tend to be borne closer to the soil surface; after a few years this may lead to weakly anchored plants.

Cultivars vary in the rate and timing of suckering, to the extent that the period between successive crops (ratoons) may differ substantially. Suckers first form a number of scale leaves and draw on the mother plant for their growth. Source-sink relations allow the sucker to form its rhizome and roots, but leaf production is held back until some time after flower initiation in the mother corm. Suckers which are held back in this way cannot change over from scales to normal leaves, but produce transitory leaves with a narrow, greatly reduced leaf blade ("sword" leaf suckers) until released. By that time the first and largest sucker usually has established dominance over the other suckers, unless pruning to retain suitably placed suckers has dictated otherwise.

Another type of sucker occurs, called water sucker. These are similar to watershoots in woody plants in the sense that their growth is not restricted by correlative inhibition; they may, for instance, be formed on the corm of a harvested stem. Water suckers form normal leaves early and these are not preceded by sword leaves; the stem is weak, matures early, and supports an inferior bunch.

Bananas produce a definite number of leaves. However, it is difficult to determine the exact number, since about one half consists of scale leaves plus sword leaves. Moreover, the eldest leaf scars are hard to trace on the corm. In most cultivars the number of normal leaves is about 30, but it may be much higher, particularly in high-density ratoon crops. The size of successive leaves increases to a maximum shortly before flowering. Thereafter the size declines until the appearance of the flag leaf signals the emergence of the inflorescence. A healthy plant has 10-15 fully functional leaves; the rate of photosynthesis is much higher in the youngest leaves. When growth is rapid, a new leaf emerges every week, replacing the eldest leaf which gradually withers. Thus bloom - or rather "shooting", i.e. the emergence of the inflorescence - may be as early as 6 months after the sucker forms its first normal leaf, but 8-9 months is more normal and under unfavourable conditions (e.g. in cool highlands or in the subtropics) this period may be twice as long. Moreover, diploid cultivars such as "Pisang Mas" have rather short cycles compared with other cultivars such as the triploid "Gros Michel".

The fruit is parthenocarpic; the ovules shrivel early but can still be recognized as brown specks in the mature fruit. The fruit growth curve is sigmoid, but during the 80-90 days from appearance of the hand until the harvest, weight increases virtually linearly. Where growth is slow this period may be much longer. As the fruit grows the pulp/skin ratio rises steadily. Since growth factors, and hence the growth rate, vary from plant to plant and the differences tend to accumulate, the uniformity of a young banana plantation quickly gives way to increasing differences in developmental stages between individual plants. The closed canopy and continuous growth of banana stands leads to much potential dry matter production. From a study of 2 plantain cultivars in Cameroon, the dry matter in the stems harvested during a year can be estimated at 30 t/ha, the harvest index - the share of the infructescences - being 47%. Total biological yield over the year is much higher as it includes the gains in underground parts, sucker weight and leaves which have been shed.

The taxonomic nomenclature of the bananas presents some special problems. In the past several specific names have been given to taxa which are now known to be fairly well-defined hybrid groups or even just cultivars. The type species of the genus, Musa paradisiaca L., the French plantain, is such a hybrid and should correctly be written as M. × paradisiaca L. or as Musa (AAB group) since it is a triploid hybrid with 2 genome sets contributed by Musa acuminata and one by Musa balbisiana. The cultivar Dwarf Cavendish has been named M. cavendishii Lambert ex Paxton (synonyms M. sinensis Sweet ex Sagot, M. nana Lour.), but being a triploid with 3 sets of genomes of M. acuminata, can be more clearly identified as Musa (AAA group) "Dwarf Cavendish". Musa chiliocarpa Backer is a hybrid belonging to M. × paradisiaca L. or the Musa (AAB group).

Simmonds suggests replacing the binomial nomenclature by a genome nomenclature as in the above examples: generic name, followed between brackets by a letter combination indicating the ploidy and the genome sets contributed by the 2 wild species, followed by the name of the cultivar group and/or the cultivar. Simmonds and Shepherd distinguished the following genome configurations:

• M. acuminata forms: AA, AAA and AAAA;
• hybrid forms: AB, AAB, ABB and ABBB.

Although they never found edible forms derived purely from M. balbisiana, the existence of M. balbisiana forms BB and BBB is suggested by morphological studies using the score-card devised by Simmonds and Shepherd to determine the genome constellation of edible bananas on the basis of 15 distinguishing characters, mostly in the inflorescences. Some cultivars in the Philippines ("Saba", the most important cooking cv.; "Abuhon"), in Thailand ("Kluai Lep Chang Kut"), in Papua New Guinea ("Auko") and possibly in Indonesia and Malaysia (respectively "Pisang Kepok" and "Pisang Nipah") score the same as M. balbisiana. Moreover, isozyme banding patterns of the cultivars also appear to be identical to those of M. balbisiana. The cultivars mentioned are triploid and may tentatively be classed in a BBB group.

Some important commercial cultivars grown in South-East Asia, grouped according to their genome constitution are:

• Musa (AA group) "Sucrier". Synonyms: "Pisang Mas" (Indonesia, Malaysia), "Kluai Khai" (Thailand), "Segale nget-pyaw" (Burma). Important in Papua New Guinea (perhaps 20 cultivars) and in Malaysia. The fruit is small with an attractive golden-yellow thin skin; the flesh is firm, light orange, aromatic and very sweet; bunches bear 5-9 hands.

• Musa (AA group) "Lakatan" (the Philippines), "Pisang Barangan" (Indonesia), "Pisang Berangan" (Malaysia - here classified as AAA group). The most popular dessert cultivar in the Philippines and also highly prized in Malaysia. Fruit medium to large, attractive golden-yellow; flesh fine, firm, dry, very sweet and aromatic; bunches bear 10-12 hands.

• Musa (AAA group) "Gros Michel". Synonyms: "Pisang Ambon" (Malaysia, Indonesia), "Avabakor", "Disu" (Papua New Guinea), "Kluai Hom Thong" (Thailand), "Thihmwe" (Burma). A high priced dessert banana in Thailand. The fruit is medium to large with thick yellow skin; the flesh is creamy white, fine textured, sweet and aromatic; bunches bear 8-12 hands.

• Musa (AAA group, Cavendish subgroup). Principal cultivars: "Dwarf Cavendish", "Giant Cavendish", "Grande Naine" and "Pisang Masak Hijau". Synonyms: "Bungulan" in the Philippines, "Pisang Ambon Lumut" in Indonesia, "Pisang Ambon Lumut" in Malaysia, "Kluai Hom Kiau" in Thailand. Widely distributed in South-East Asia. The fruit is medium to large with light green to greenish-yellow skin; the flesh is white to creamy, soft, finely-textured and sweet; bunches bear 8-12 hands. In the Philippines "Giant Cavendish" is the major cultivar for the export market. The fruit is large with a thick skin, ripening yellow at low temperatures (in storage), normally ripening greenish-yellow; bunches bear 14-20 hands.

• Musa (AAA group) "Pisang Ambon Putih" (Indonesia), "Pisang Embun" (Malaysia), "Ambon" (the Philippines), "Kluai Hom Dok Mai" (Thailand). The most important cultivar in Indonesia. Fruits large with yellow smooth skin; flesh creamy, moderately firm, slightly aromatic, sweet; bunches bear 10-14 hands.

• Musa (AAB group) "Silk". Synonyms: "Pisang Rastali" (Malaysia), "Pisang Raja Sereh" (Indonesia), "Woradong", "Maramba", "Avundumong" (Papua New Guinea), "Latundan", "Tundan", "Dr Turdan", "Cantong" (the Philippines), "Htaw-bat" (Burma). The most popular dessert cultivar in Indonesia and Malaysia. Fruit small to medium, yellow; flesh white, soft, finely textured, slightly subacid; bunches bear 5-9 hands.

• Musa (AAB group) "Pisang Raja". Synonyms: "Pisang Raja" (Indonesia, Malaysia), "Radja" (the Philippines), "Larip", "Houdir", "Kalamanawudu" (Papua New Guinea). Highly prized in Indonesia; grown in the Philippines and Malaysia as a cooking banana. Fruits large with thick coarse skin, orange; flesh creamy-orange, texture coarse, taste sweet; bunches bear 6-8 hands.

• Musa (AAB group, Plantain subgroup) "Horn". Synonyms: "Pisang Tanduk" (Indonesia), "Pisang Tanduk" (Malaysia), "Tindok" (the Philippines), "Kluai Nga Chang" (Thailand). The cultivar with the largest fruits. Commercially it is important in Indonesia (Java). The banana requires some cooking to become palatable. Skin yellow; flesh light creamy-orange, firm, fine in texture, remains starchy; good keeping quality; bunches with 2 hands. This cultivar has no persistent male bud.

• Musa (ABB group) "Pisang Awak". Synonyms: "Pisang Siem" (Indonesia), "Pisang Awak" (Malaysia), "Katali" (the Philippines), "Kluai Namwa" (Thailand), "Yakhine" (Burma). "Kluai Namwa" is important and widely grown in Thailand. Fruit small to medium, yellow; skin medium thick, flesh firm, white, sticky, edible fresh or cooked; bunches bear 8-10 hands.

• Musa (ABB group) "Bluggoe". Synonyms: "Pisang Kepok" (Indonesia), "Pisang Abu Keling" (Malaysia), "Kluai Hak Muk" (Thailand). Favourite cooking banana in Thailand. The fruits are always cooked before consumption. Fruit medium to large; skin thick, coarse, turning brownish-yellow when ripe; flesh creamy orange and starchy; bunches bear 7 hands.

• Musa (BBB group) "Saba". Synonyms: "Saba", "Cardaba" (the Philippines), "Kluai Hin" (Thailand), perhaps also "Pisang Kepok" (Indonesia; the name is used for different forms, some with ABB characteristics, others possibly belonging to the BBB group), "Pisang Nepah" (Malaysia). Most important cultivar in the Philippines, primarily used as a cooking banana. Fruit medium to large, stout and angular; skin thick, yellow; pulp creamy-white, finely textured, with a well-developed core, sweet; bunches bear 10-16 hands.

Since a continuously high growth rate leads to high yield, banana is at its best in warm and humid tropical climates. However, the crop is so attractive that it is grown right up to its ecological limits, where the mean growth rate affords marginal yields. Temperature is a major factor. In none of the important production centres does the temperature drop below 15 °C for long; the optimum for growth is about 27 °C and the maximum 38 °C. Chilling injury occurs below 13 °C and only "Mysore", "Dwarf Cavendish" and "Pome" tolerate temperatures near 0 °C. In the equatorial highlands the banana disappears at elevations above 1600 m.

Radiation requirements are not clearly understood. Most bananas grow best in full sun, but excessive exposure causes sunburn. Under overcast conditions or light shade the growth cycle is somewhat longer and the bunch smaller. Banana is sensitive to strong wind which shreds the leaves, causes crown distortions and blows plants over.

A steady moisture supply is required; for optimum growth the monthly rainfall should be 200-220 mm and soil moisture should not be depleted below 60-70% of field capacity; hence most areas benefit from (supplementary) irrigation. The best soil for banana is a deep, friable loam with good drainage and aeration. High fertility is a great advantage and organic matter content should be 3% or more. The plant tolerates pH values of 4.5-7.5.

Bananas are generally propagated by suckers. Sword leaf suckers are preferred since they bear larger bunches in the first crop (the "plant crop"). Corms or pieces of corms ("bits") are also used as planting material. They are usually pared and may be immersed in hot water (52 °C) or a pesticide solution to kill nematodes and borers before planting. Recently, tissue culture for rapid propagation through disease-free shoot tips has been developed. This method is already employed commercially, but the occurrence of undesirable mutations is causing concern.

Densities range from 1000-3000 plants/ha, depending mainly on the cultivar. Equidistant planting patterns and row cropping are both practised; planting in double rows makes it possible to combine dense populations with good access, e.g. (3.5 + 1.5) m × 2 m = 10 m²/2 plants or 2000 plants per ha and 3.5 m wide alleys. Planting is generally done at the onset of the rainy season. Planting material is usually set 30 cm deep.

Banana is grown in four distinct cropping systems, namely: home gardens, mixed cropping systems in farmers' fields, commercial smallholder orchards, and corporate plantations. In home gardens a wide variety of cultivars - depending on the region - is grown for home consumption, using minimal inputs. Surplus produce is sold in the market. This is the most common cropping system in South-East Asia. Banana is either the principal or the auxiliary crop in mixed cropping systems. It is commonly planted as a nurse crop for young cocoa, coffee, black pepper, etc. It is also used as an intercrop in newly established rubber and oil palm plantations, and under mature coconut. When grown as the principal crop, it is usually interplanted with annual crops.

In smallholder orchards banana is grown as a sole crop in areas ranging from 1.5-20 ha. The choice of cultivars depends on consumer's preference and suitability to prevailing agroclimactic conditions in the area. Management practices include manuring, weeding, deleafing, replanting and crop protection.

Corporate plantations cater for the export markets. It is a capital- intensive system involving heavy investment in infrastructure including drainage networks, roads, cableways, packing houses, piers, airstrips and office and service buildings. Intensive husbandry ensures high yield and good quality to meet the strict requirements of the export market. Commonly a single cultivar is grown in large tracts of land.

Frequent weeding is required until the plants shade out weeds. Weeds are controlled by mechanical means (slashing, hoeing, etc.) or by hand. Pre-emergence herbicides are effective, and when the plants attain a height of 1.5 m or more, contact herbicides can be used.

Banana needs large quantities of nutrients. Nutrient removal by a crop of 30 t/ha amounts to 50 kg N, 15 kg P₂O₅, 175 kg K₂O, 10 kg CaO and 25 kg MgO. In home gardens the application of manures and compost is recommended together with 0.25 kg of urea and muriate of potash every three months for each stool. Commercial plantations monitor the leaf nutrient level, sampling the third youngest leaf. The following levels - in dry matter percentage - are considered adequate: N 2.6, P₂O₅ 0.45, K₂O 4.0, CaO 1.40, and MgO 0.60.

Irrigation is necessary in areas with a long dry season but also if rainfall is less than 200-220 mm per month. Water can be applied by furrow or sprinkler irrigation; recently, drip irrigation has gained acceptance. During a weekly pruning round, withering leaves are cut to provide mulch and to eliminate sources of infection by leaf diseases.

In commercial plantations several other practices are carried out to sustain high productivity and ensure good quality fruit for the (export) market. These are desuckering, propping, removal of male buds, and bagging of the bunch. Every 6-12 weeks plants are desuckered to leave only the mother stem (bearing), a daughter (the follower) and - in the case of ratoons - a grand-daughter. At low density, each stool can carry 2 mother stems and 2 followers. Thus, to prevent overcrowding and to regulate the successive crops per stool, a follower is spared for each mother stem every 6-10 months (or more in cool climates) to bear the next bunch. Only healthy, deep-set suckers are spared. Props or ties provide additional support for the plants when the bunches appear; they prevent the plant from being toppled by the heavy weight of the bunch. The male bud is removed as soon as the last two hands of the bunch appear. At the same time, one or more hands may be removed to increase finger length in the remainder, and bunches may be bagged. The bags are polythene sleeves impregnated with insecticides; they are used to prevent fruit blemishes from insects, birds, dust, etc., and to raise the temperature of the bunch, advancing fruit growth, particularly in cooler climates.

Yellow Sigatoka or leaf spot is one of the most important diseases. It is caused by Mycosphaerella musicola (conidial stage, Cercospora musae) which is endemic to South-East Asia and is only found on banana. Leaf-spots cause premature death of large areas of foliage, resulting in a smaller bunch with fewer hands and small unfilled fingers. A more virulent form of leaf-spot, namely the black Sigatoka caused by M. fijiensis var. difformis, is now coming to the fore in the Philippines, Taiwan, Papua New Guinea and eastern Indonesia. The main Cavendish group cultivars are very susceptible. Spores are released and become infective only when the leaf is wet. Measures which prevent formation of dew and lower leaf temperature (e.g. shade trees) limit the spread of these diseases. It is hard to obtain adequate coverage with fungicides, except by aerial spraying or powerful mist blowers.

Fusarium wilt or Panama disease is caused by Fusarium oxysporum f. cubense. It is a soilborne fungus, which attacks the roots of susceptible cultivars and blocks the vascular system, so that the plant wilts. The only control measure is the physical or chemical (herbicide) destruction of infected plants and their neighbours; the plot should be fallowed, fenced, and excluded from cultivation and the passage of water. Races I, II and III of fusarium wilt affect bananas within the region. Race I has caused severe losses in cultivars such as "Gros Michel" and "Silk". Now the appearance of race IV in Taiwan and the Philippines poses a threat to the Cavendish cultivars.

Bacterial wilt or Moko disease is caused by Pseudomonas solanacearum and can kill an infected banana plant in just a few weeks. At present four "biovars" are recognized, of which biovars 1 and 3 attack banana and Heliconia spp. The bacteria can be transmitted through mechanical means, but biovar 1-SFS is an insect-transmitted strain and regarded as the most contagious form. Control involves the disinfection of all tools used in various farm operations, and destruction of infected and neighbouring plants. Fumigation and quarantine of the affected area is strongly recommended. The disease is common in the western hemisphere; in South-East Asia it occurs only in the Philippines (Mindanao). Virus diseases include bunchy top, mosaic and bract mosaic. Both bunchy top and mosaic are transmitted by aphids (the banana aphid (Pentalonia nigronervosa) causes bunchy top; the corn aphid (Rhopalosiphum maidis) and the cotton aphid (Aphis gossypii) are the vectors for mosaic). Control of these diseases involves quarantine, regular inspection and destruction of diseased plants, use of virus-free planting material, removal of alternative hosts, and control of the vectors.

The most important insect pest is the banana weevil borer (Cosmopolites sordidus). It is native to South-East Asia and had spread to all banana- growing areas. The larva is most destructive: it bores into the corm and pupates in the tunnels formed. A large portion of the tissues is destroyed, thereby lessening the uptake of water and nutrients as well as the anchorage of the plants. Adults lay their eggs on or near corm tissue. Control measures include chopping up of the corm and pseudostem to hasten decomposition, trapping and collecting the adults, using non-infested planting material, destroying the shelter and feeding places of the adult weevil by maintaining a clean area around the mat and applying insecticides. Two kinds of thrips attack the banana plant. The flower thrips, Thrips florum, is small and can enter the developing fruit while the bracts are still present. It oviposits and feeds on the young fruit, resulting in a rough skin and sometimes a cracked fruit. The red rust thrips, Chaetanaphothrips signipennis, feeds on the area where adjacent fingers touch, resulting in a reddish discolouration. Insecticides or bunch covers are used to control these pests; encouraging colonies of ants may also be helpful.

The burrowing nematode (Radopholus similis) is the most destructive nematode species. Dark patches or spots on the roots indicate attack and subsequent fungal infection. Severely infected plants may show only stubs of rotted roots and may fall down when the bunch has formed. Control measures include removing infected plants, using nematode-free planting material and resistant cultivars, applying nematicides and biological control by Paecilomyces lilacinus, a fungus which parasitizes the egg, larva and adult.

The fruit is harvested more or less green. The stage of maturity is judged by the angularity of the fingers: the more rounded a finger is in cross-section, the more mature it is. While fruit weight increases rapidly as angularity is lost, the fruit also becomes more vulnerable to damage during transport and it does not keep as long, so it has to be picked early. For the export market the fruit is harvested 10-14 weeks after flower emergence, when the middle finger of the outer whorl of the second proximal hand in the bunch attains a diameter of 32-38 mm; the larger diameter applies when the fruit is expected to be shipped quickly to the export market. Undersized fruit in the harvested crop is sold locally or dumped.

Two people, a harvester and a backer, collect the crop. The backer carries a shoulder pad to cushion the fall of the bunch after the harvester has nicked the stem with a machete so that the top of the plant with the bunch keels over. A bamboo pole is used to support the bunch until it touches the shoulder pad. Once the bunch is lowered in this way, the harvester cuts the bunch, leaving an ample length of peduncle to serve as a handle. The bunches are then transported carefully to the packing house by cable system or tractor-drawn padded trailers.

Yield is extremely variable, ranging from 3-60 t/ha per year, depending largely on the cultivar and the cropping system. Yields of 140 t/ha and more have been recorded in experiments with the leading world cultivars, but such extreme figures refer to a shoot-to-shoot period of 1.5-2 years. Cultivars of the Cavendish group are by far the most productive; for these cultivars, 100 t/ha per year appears to be a realistic goal. In northern Queensland, data on the plant crop and 2 ratoon crops were collected for 21 cultivars, including cultivars from South-East Asia. The trial confirmed the homogeneity and superiority of the 8 Cavendish cultivars, for instance, as expressed in kg fruit per m pseudostem height: 14-18 kg/m for the Cavendish group in comparison with 3.5-9 kg/m for the other cultivars. There is an urgent need for more information on the yield and yield components of high-quality South-East Asian cultivars.

The harvested bunches are dehanded, and the hands are deflowered, washed, sorted, and packed in carton boxes for export. In addition, the fruit is treated with fungicides to prevent the fruit cushions from rotting. Storage life of green bananas ranges from 21-30 days at 13-15°C. Calcium carbide (CaC₂) at 0.29 g/l or ethephon solution (500-1000 mg/l depending on the cultivar) may be used to ripen green mature fruits. In the former treatment, the fruit is exposed for 24-36 h in an enclosed container whereas with the latter, a 5 minute dip is effective. Ethylene gas is used in large commercial operations. The bananas are treated for 24 h in a closed chamber containing 1000 mg/l ethylene and the temperature is maintained at 14-18°C. Every 24 h the chamber is opened for ventilation until the fruit has reached a marketable colour.

South-East Asia is the centre of diversity of banana. A regional collection of germplasm is being maintained at the Davao National Crop Research and Development Center, Bureau of Plant Industry, Davao City, the Philippines. In addition, national collections of cultivars are maintained in Malaysia (MARDI), Thailand (Kasetsart University), Indonesia (Cibinong, Tlekung and Purwodadi) and the Philippines (UPLB). Outside South-East Asia there are regional collections in Jamaica and Cameroon. National collections exist in many countries.

Limited work has been undertaken to develop new cultivars in the region, most research being concentrated on characterizing the various cultivars/accessions present in each country. The possibility of induced mutation breeding in conjunction with tissue culture techniques is now being explored. Breeding programmes are under way in Nigeria, Honduras and Brazil. The main objective is to obtain cultivars resistant to black Sigatoka, fusarium wilt and nematodes, while retaining acceptable fruit quality, high yield and a manageable plant habit.

Banana is important for South-East Asia in both the local and the export markets. In the local market banana is the principal fruit. As it is relatively cheap and available throughout the year, the poor person's fruit intake depends heavily on the banana. There appears to be ample room for increased local consumption if efficient production makes the fruit still cheaper. Virus diseases go virtually unchecked and form a threat for banana production in the region. Disease- and nematode-resistant cultivars are important to raise yield levels and efficiency, particularly in the small-scale cropping systems; other yield-limiting factors need to be identified and overcome.

The world market has been on the brink of overproduction for a long time; nevertheless during the 1970s production in South-East Asia increased by 68%, mainly because of expanding export production in the Philippines. Neighbouring countries are developing their capability to enter export markets, but in the 1980s production in the region stagnated while population growth pushed up domestic demand. It is hard to predict developments in world trade, but a positive point is that processed products such as chips, crackers and purees have gained acceptance both in domestic and export markets. Moreover, there appears to be a growing interest overseas in the high-quality cultivars of the Musa (AA group), e.g. the "Pisang Mas". Banana research has always been largely directed towards Musa (AAA group) cultivars, the leaders in world trade. Little is known about the other groups which all have their own scope and limitations with respect to production and markets. Cultivars of these groups deserve more attention, particularly in South-East Asia, a primary centre of diversity. The International Network for the Improvement of Banana and Plantain (INIBAP) provides an international setting for efforts in this direction.

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• R.R.C. Espino, S.H. Jamaluddin, Bechamas Silayoi & R.E. Nasution